bims-lypmec 2024-07-21 papers

Issue of 2024‒07‒21
four papers selected by
Satoru Kobayashi, New York Institute of Technology

J Biol Chem. 2024 Jul 14. pii: S0021-9258(24)02076-3. [Epub ahead of print] 107575

Phosphorylation of GCN2 by mTOR confers adaptation to conditions of hyper-mTOR activation under stress.

Odai Darawshi, Olaya Yassin, Miri Shmuel, Ronald C Wek, S Jalil Mahdizadeh, Leif A Eriksson, Maria Hatzoglou, Boaz Tirosh.

Adaptation to shortage in free amino acids (AA) is mediated by two pathways, the integrated stress response (ISR) and the mechanistic target of rapamycin (mTOR). In response to reduced levels, primarily of leucine or arginine, mTOR in its complex 1 configuration (mTORC1) is suppressed leading to a decrease in translation initiation and elongation. The eIF2α kinase general control nonderepressible 2 (GCN2) is activated by uncharged tRNAs, leading to induction of the ISR in response to a broader range of AA shortage. ISR confers a reduced translation initiation, while promoting the selective synthesis of stress proteins, such as ATF4. To efficiently adapt to AA starvation, the two pathways are cross-regulated at multiple levels. Here we identified a new mechanism of ISR/mTORC1 crosstalk that optimizes survival under AA starvation, when mTORC1 is forced to remain active. mTORC1 activation during acute AA shortage, augmented ATF4 expression in a GCN2-dependent manner. Under these conditions, enhanced GCN2 activity was not dependent on tRNA sensing, inferring a different activation mechanism. We identified a labile physical interaction between GCN2 and mTOR that results in a phosphorylation of GCN2 on serine 230 by mTOR, which promotes GCN2 activity. When examined under prolonged AA starvation, GCN2 phosphorylation by mTOR promoted survival. Our data unveils an adaptive mechanism to AA starvation, when mTORC1 evades inhibition.

DOI: https://doi.org/10.1016/j.jbc.2024.107575

Physiology (Bethesda). 2024 Jul 16.

The Spectrum of "TFEopathies" - Flipping the mTOR Switch in Renal Tumorigenesis.

Nicola Alesi, Kaushal Asrani, Tamara L Lotan, Elizabeth P Henske.

The Mammalian Target of Rapamycin Complex 1 (mTORC1) is a serine threonine kinase that couples nutrient and growth factor signaling to the cellular control of metabolism and plays a fundamental role in aberrant proliferation in cancer. mTORC1 has previously been considered an "on/off" switch, capable of phosphorylating the entire pool of its substrates when activated. However recent studies have indicated that mTORC1 may be active towards its canonical substrates, 4EBP1 and S6K, involved in mRNA translation and protein synthesis, and inactive towards TFEB and TFE3, transcription factors involved in the regulation of lysosome biogenesis, in several pathological contexts. Among these conditions are Birt Hogg Dube (BHD) and recently, Tuberous Sclerosis Complex (TSC). Furthermore, TFEB and TFE3 hyperactivation in these syndromes, and in translocation Renal Cell Carcinomas (tRCC), drives mTORC1 activity towards the canonical substrates, through the transcriptional activation of the Rag GTPases, thereby positioning TFEB and TFE3 upstream of mTORC1 activity towards 4EBP1 and S6K. The expanding importance of TFEB and TFE3 in the pathogenesis of these renal diseases warrants a novel clinical grouping that we term "TFEopathies". Currently, there no therapeutic options directly targeting TFEB and TFE3, which represents a challenging and critically required avenue for cancer research.

Keywords: Kidney TFEopathies; TFE3; TFEB; TSC; mTORC1

DOI: https://doi.org/10.1152/physiol.00026.2024

Biochem Pharmacol. 2024 Jul 16. pii: S0006-2952(24)00421-0. [Epub ahead of print] 116438

Inhibition of PLA2G4A attenuated valproic acid- induced lysosomal membrane permeabilization and restored impaired autophagic flux: Implications for hepatotoxicity.

Ming-Lu Wang, Yu-Jia Zhang, Da-Long He, Tong Li, Ming-Ming Zhao, Li-Mei Zhao.

Valproic acid (VPA) has broad efficacy against several seizures but causes liver injury limiting its prolonged clinical use. Some studies have demonstrated that VPA-induced hepatotoxicity is characterized by microvesicular hepatic steatosis. However, novel detailed mechanisms to explain VPA-induced hepatic steatosis and experimentally rigorously validated protective agents are still lacking. In this study, 8-week-old C57BL/6J mice were gavaged with VPA (500 mg/kg/d) for 4 weeks to establish an in vivo model of VPA-induced chronic liver injury. Quantitative proteomic and non-targeted lipidomic analyses were performed to explore the underlying mechanisms of VPA-induced hepatotoxicity. As a result, VPA-induced hepatotoxicity is associated with impaired autophagic flux, which is attributed to lysosomal dysfunction. Further studies revealed that VPA-induced lysosomal membrane permeabilization (LMP), allows soluble lysosomal enzymes to leak into the cytosol, which subsequently led to impaired lysosomal acidification. A lower abundance of glycerophospholipids and an increased abundance of lysophospholipids in liver tissues of mice in the VPA group strongly indicated that VPA-induced LMP may be mediated by the activation of phospholipase PLA2G4A. Metformin (Met) acted as a potential protective agent attenuating VPA-induced liver dysfunction and excessive lipid accumulation. Molecular docking and cellular thermal shift assays demonstrated that Met inhibited the activity of PLA2G4A by directly binding to it, thereby ameliorating VPA-induced LMP and autophagic flux impairment. In conclusion, this study highlights the therapeutic potential of targeting PLA2G4A-mediated lysosomal dysfunction in VPA-induced hepatotoxicity.

Keywords: Autophagy; Cytosolic phospholipase A2; Lysosomal membrane permeabilization; Metformin; Valproic acid

DOI: https://doi.org/10.1016/j.bcp.2024.116438

Cell Mol Life Sci. 2024 Jul 15. 81(1): 304

Truncated tau interferes with the autophagy and endolysosomal pathway and results in lipid accumulation.

Saskia J Pollack, Dina Dakkak, Tong Guo, George Chennell, Patricia Gomez-Suaga, Wendy Noble, Maria Jimenez-Sanchez, Diane P Hanger.

The autophagy-lysosomal pathway plays a critical role in the clearance of tau protein aggregates that deposit in the brain in tauopathies, and defects in this system are associated with disease pathogenesis. Here, we report that expression of Tau35, a tauopathy-associated carboxy-terminal fragment of tau, leads to lipid accumulation in cell lines and primary cortical neurons. Our findings suggest that this is likely due to a deleterious block of autophagic clearance and lysosomal degradative capacity by Tau35. Notably, upon induction of autophagy by Torin 1, Tau35 inhibited nuclear translocation of transcription factor EB (TFEB), a key regulator of lysosomal biogenesis. Both cell lines and primary cortical neurons expressing Tau35 also exhibited changes in endosomal protein expression. These findings implicate autophagic and endolysosomal dysfunction as key pathological mechanisms through which disease-associated tau fragments could lead to the development and progression of tauopathy.

Keywords: Alzheimer’s disease; Autophagy; Dementia; Endosomes; Lysosomes; TFEB; Tau

DOI: https://doi.org/10.1007/s00018-024-05337-6